Pontoon type floating roof for liquid storage tank

ABSTRACT

A pontoon type floating roof for liquid storage tanks comprises a pontoon ring, an annular tension buffer assembly disposed concentric with respect to the pontoon ring, and a roof deck connected between the pontoon ring and side walls of the tension buffer assembly. The center part of the roof deck is located lower than the horizontal plane that includes the pontoon ring and the tension buffer assembly so that rainwater, oil, or the like accumulated on the roof drains away.

United States Patent Iwagami et al. 1 July 1, 1975 [5 1 PONTOON TYPE FLOATING ROOF FOR 2.281772 5/1942 Wiggins 220/211 R LIQUID STORAGE TANK 2.321.058 6/1943 Wigginsm 2172,1305 12/1956 Grundig 220/26 R 1 lnvemorsl Masao g i, Toky Saloshi 2.8011958 10/1957 Wiggins 220/26 R Miyashita, Yokohama, both of 1374.918 3/1968 Creith Japan 3.424.335 1/1969 Wiltshire 3 724 704 4/1973 Edwards et a1. .0 220/26 R [73] Asslgnee: Chiyoda Kako Kensetsu Kabushiki Japan Primary Examiner-John Petrakes [22] Filed: Oct. 17, 1973 Attorney, Agent, or Firm-Connolly and Hutz [211 App]. No.: 407,272

[57] ABSTRACT [30] Foreign Application Priority Data A pontoon type floating roof for liquid storage tanks Oct 20 972 Japan u 47404395 comprises a pontoon ring, an annular tension buffer assembly disposed concentric with respect to the pon- 521 U.S. c1 220/219; 220/216 ring and a roof deck Connected. 51 1111. c1 B65d 87/18 and Side of sembly. The center part Of the roof deck IS located 220/227 114/127 lower than the horlzontal plane that lncludes the puntoon ring and the tension buffer assembly so that rain- [56] References Cited water. oil, or the like accumulated on the roof drains away.

12 Claims, 8 Drawing Figures PONTOON TYPE FLOATING ROOF FOR LIQUID STORAGE TANK BACKGROUND OF THE INVENTION The present invention relates to pontoon type floating roofs for liquid storage tanks, and more particularly to pontoon type floating roofs for liquid storage tanks which prevent the roof from being damaged due to the load ofa large volume of rainwater. oil or the like accumulated on the floating roof at emergency times.

A floating roof tank has been used for storing highly volatile liquid such as crude oil and gasoline. Recently, the capacity of the floating roof tank has rapidly increased with increase in the consumption of petroleum and the capacity of a tanker which is to transport a great volume of petroleum. This has given rise to the problem that the pontoon type floating roof is sunk or destroyed due to loads by rainwater or petroleum accumulated on the roof.

SUMMARY OF THE INVENTION An object of the present invention is to provide a safety pontoon type floating roof for liquid storage tanks which prevents the rooffrom being damaged due to loads such as rainwater or petroleum accumulated thereon.

Another object of the invention is to provide a pontoon type floating roof for liquid storage tanks which is capable of effectively and rapidly draining liquid, such as, for example, rainwater, which might otherwise accumulate on the roof.

Another object of the invention is to provide a pontoon type floating roof for liquid storage tanks with an annular tension buffer assembly which reduces the radial inward load exerted on a roof deck due to loads created by rainwater or petroleum accumulated on the roof.

Still another object of the invention is to provide a pontoon type floating roof for liquid storage tanks which prevents the roof from an unbalanced accumulation of rainwater or petroleum by means of pipes communicating with the rainwater drain sumps under the roof deck and with the inside and outside ofthe annular tension buffer assembly.

In accordance with the present invention a pontoon type floating roof for liquid storage tanks comprises a pontoon with at least one annular tension buffer assembly concentrically disposed within and with respect to the pontoon. A roof deck extends between the pontoon and the annular tension buffer assembly, and a roof deck is also provided within the annular tension buffer assembly. The pontoons and the annular tension buffer assembly include elastically deformable side walls to which the roof decks are connected.

BRIEF DESCRIPTION OF THE DRAWINGS Novel features and advantages of the present invention in addition to those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

FIG. 1 is a longitudinal sectional view of a pontoon type floating roof and a liquid storage tank, according to the present invention;

FIG. 2 is a top plan view of the structure shown in FIG. I;

FIG. 3 is a longitudinal sectional view of a conventional pontoon type floating roof tank;

FIG. 4a through 4c are sectional views showing different annular tension buffer assemblies, according to the present invention;

FIG. 5 is a longitudinal sectional view showing the side wall of the pontoon ring connected to the deck plate, according to the present invention; and

FIG. 6 is a conceptional longitudinal sectional view of a pontoon type floating roof of another embodiment of the invention illustrated in connection with the instance that rainwater is accumulated on the roof.

DETAILED DESCRIPTION OF THE INVENTION A typical conventional pontoon type floating roof and the design basis and the problems for strength of the floating roof at emergency will first be described for better understanding of the invention. Referring to FIG. 3, there is shown a sectional view of a conventional pontoon type floating roof. Generally, this type of roof has a pontoon ring a (hereinafter referred to as pontoon) around the roof, and/or is equipped with a cylindrical pontoon b in the center of the roof deck.

Meanwhile, the following requirements for the design of a pontoon type floating roofs are specified in AP] STD 650, APPENDIX C, paragraph C.3.4.

a. The minimum pontoon volume of a single-deck pontoon roof shall be sufficient to keep the roof floating on a liquid with a specific gravity of 0.7 if the single deck and any two pontoon compartments are punctured. The primary drainage shall be considered as inoperative, but no live load need be considered for the preceding design requirements.

b. In addition, a single-deck pontoon roof with the primary drainage inoperative shall accommodate a 10 inch rainfall in a 24-hour period over the entire roof area without sinking (with no compartments or decks punctured). The roof may be designed to carry the entire 24-hour rainfall, or emergency drains may be installed which will limit the roof load to some lesser volume of water which the roof will safely carry. Such emergency drains shall not allow the product to flow onto the roof deck.

For example, assuming that rainwater accumulates on the roof deck 0, and the roof load of the rainwater exceeds the exerted buoyancy on the roof deck c in FIG. 3, and then the roof deck c largely deflects and a radial inward load q occurs in the direction of arrow x on the side wall e where the roof deck c is joined to the pontoon a because of unbalanced loading between the roof deck portion and the pontoon portion. When the radial inward load q increases, a lateral torsional buckling occurs on the entire pontoon 0 because the pontoon a is annular and flat (for example, 600 to 800 mm high and 3 to 8 m wide).

The critical radial inward load Q, in kg/cm, against the lateral torsional buckling of the entire pontoon a is calculated from the following approximate formula;

k is the coefficient depending on the condition of stiffness of the pontoon a,

I is the least moment of inertia of the cross section of the pontoon a in cm, and

R is the mean radius of the pontoon ring a in cm.

Since the critical radial inward load Q is inversely proportional to the cubic power of the mean radius R of the pontoon ring a, as indicated by the above formula, this critical radial inward load Q is extremely small on a large tank. While the radial inward load q in kg/cm is approximately calculated from the following formula;

E \l 1 I z where E is the modulus of elasticity of the material in kg/cm r is the thickness of the roof deck c in cm.

I is the original length of the roof deck in the radial direction in cm, and

A1 is the elongation of the roof deck 0 in the radial direction in cm.

For example, assuming a tank about 80 min diameter where E 2.l l() (kg/cm and I 0.45 (cm) Then the radial inward load q is I.3SX]() AI (kg/cm) Therefore, when the roof deck 0 is elongated by 1 cm, the radial inward load q will become 135 (kg/cm) and this large radial inward load will cause damage of the inner wall part c of the pontoon a or lateral torsional buckling of the entire pontoon a.

The principle for reduction of the radial inward load q on a pontoon type floating roof under the invention is described below.

When rainwater is accumulated on the roof, the roof deck will deform downward and the rainwater load plus the weight of roof deck 0 will balance with the buoyancy occurred on the roof deck portion plus the pulling load due to the radial inward load q.

Accordingly, under the same load condition of rainwater, the pulling load or the radial inward load q will decrease with increase of the buoyancy occurred on roof deck portion, namely the deformation of the roof deck 0.

The following methods to obtain large deformation of the roof deck 0 for the purpose of the reduction of radial inward load q will be considered;

METHOD l To design and install the roof deck c of which the actual radial length is longer than the calculated radial length in horizontal plane, for example, to provide the roof deck c' with original deformation such as wave shape, or to install the roof deck c on a temporary roof staging with slope such as cone down staging.

METHOD 2 To design and install an assembly (or assemblies) which functions to reduce the radial inward load q as the result that an elastic deflection or deformation of a part of (or whole) the assembly due to the radial in ward load q will replace the elongation of the roof deck 0 to obtain a large deformation of the roof deck c. (The assembly will hereinafter be referred to as the tension buffer assembly).'

Also, these methods are efiective for reduction of the radial inward load q on the condition of the puncture of the roof deck 6 because the large deformation of the roof deck rcauses an enlargement of angle between the roof deck 0 and the horizontal line at the joint of the roof deck c connected to the wall of the pontoon a. With consideration of a normal operation of a petroleum storage tank, the rainwater falling on a roof deck 0 of a floating roof designed and installed by applying method I stands on the lower parts of the roof deck 0 deformed originally and/or secondarily, a bad drainage condition results and a painting on the roof deck c is damaged.

Furthermore, a pontoon type tension buffer assembly shown in FIGS. 40 and 4b is able to reduce the radial inward load q because of a reduction of roof loads onto the pontoon a.

Accordingly, the application of the tension buffer assembly for the pontoon type floating roof is the best effective way for the reduction of the radial inward load Referring to FIG. 1, there is shown a sectional diagram for illustrating a pontoon type floating roof for liquid storage tank, which is one of the embodiments of the present invention. This floating roof comprises a pontoon l which corresponds to the above described pontoon a, an annular tension buffer assembly 2 having a circular shape being concentric with the pontoon 1, an annular intermediate portion 3 between the pontoon l and the tension buffer assembly 2, and a roof deck 5' disposed inside 4 of the tension buffer assembly 2. A roof deck 5 is joined to side walls 6 and 7 of the pontoon l and tension buffer assembly 2. The side walls 6 and 7 are similar to the structure shown in FIG, 4a and these walls elastically deflect when a radial inward load q occurs on the roof deck 5. The roof deck 5' is joined to the inner wall 7' of the tension buffer assembly 2. The inner wall 7' elastically deflects when a radial inward load q is exerted on the roof deck 5, as in FIG. 4a. The tension buffer assembly 2 may be one shown in FIGS. 4b and 46. Also, as shown in FIG. 5, knuckle rings 10 and 11 may be used to hold one of the tension buffer assembly or the pontoon and the roof deck 5 whereby the pontoon 1 is joined to the roof deck 5. In this structure, the ring 11 may be omitted, or the knuckle ring may be constructed integral with the inner part of the upper plate of the pontoon 1. In FIG. 1, nu meral 16 indicates the floating roof support.

This embodiment is very useful because when rainwater is accumulated on the roof deck, elastic deflection or deformation is brought about in the side walls 7 and 7' of the annular tension buffer assembly 2, the annular tension buffer assembly g shown in FIGS. 4b and 4c, and/or the rings 10 and 11 shown in FIG. 5 to cause the roof deck 5 and 5 to be largely deformed, and hence there are no possibilities of allowing the large radial inward load for the pontoon 1 to be damaged.

An annular tension buffer assembly 2 having a closed hollow section as shown in FIGS. 40 and 4b is also highly advantageous for effective drainage of rainwater on the roof since the length of drain path is considerably reduced in comparison with that of a conventional pontoon type floating roof. A drainage system of a floating roof with the annular tension buffer assembly is as follows. The center part of the roof decks 5 and 5, i.e., the center part 8 of the annular intermediate portion 3. and the center part 9 of the inside 4 are located below the horizontal plane M which includes the connections of the roof decks 5 and 5' to the pontoon l and the small annular tension buffer body 2, as shown in FIG. 6. Due to a buoyancy of the annular tension buffer assembly, a main drain sump 12 is disposed in the lower position thereof and connected to a roof drain system 14, as shown in FIGS. 2 and 6. An auxiliary drain sump 13 is provided which communicates with the main drain sump 12. As shown in FIG. 4a, a pipe 15 is extended from the inner wall 7' to the outer wall 7 to permit rainwater to pass through between the roof decks 5 and 5' and thus the load of rainwater is balanced. ln this embodiment, one annular tension buffer assembly is used. Altematively. a plurality of annular tension buffer assemblies may be used in concentric arrangement when the diameter of the tank is large. Although it is best for the tension buffer assembly to be annular in view of uniform distribution of stress when the tank is cylindrical, the tension buffer assembly may be polygonal. Also. the tension bufier assembly may be split into a plurality of the assemblies.

What is claimed is:

l. A pontoon type floating roof for liquid storage tanks comprising a pontoon, at least one annular tension buffer assembly concentrically disposed within and with respect to the pontoon, and roof decks located at or under the level of liquid stored in a tank extending between the pontoon and the annular tension buffer assembly and also within the annular tension buffer assembly, the roof decks having a lower surface in continuous contact with the stored liquid to prevent the formation and accumulation of vapor under the decks. and wherein the pontoon and the annular tension buffer assembly include elastically deformable side walls to which the roof decks are connected.

2. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the roof decks are connected to the side wall of the pontoon by means of a ring member having a curved section.

3. A pontoon type floating roof for liquid storage tanks as in claim I wherein the roof decks are held by a pair of upper and lower knuckle rings fitted to the side walls of the pontoon whereby the roof decks are integrated with the pontoon.

4. A pontoon type floating roof for liquid storage tanks as in claim 3 wherein the knuckle rings fitted to the side walls of the pontoon are disposed on the top of the roof decks and integrated with the roof decks.

5. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the inner portion of the top plate of the pontoon is formed into a knuckle ring and the roof decks are fitted to the ends of this ring.

6. A pontoon type floating roof for liquid storage tanks as in claim 5 wherein the knuckle ring is a ring of A round.

7. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the cross section of the annular tension buffer assembly is cylindrical.

8. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the cross section of said annuiar tension buffer assembly is semi-cylindrical.

9. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the annular tension buffer assembly is a closed hollow annular structure, and the center portions of the roof decks disposed between the pontoon and the annular tension buffer assembly and within the annular tension bufi'er assembly are located below a horizontal plane which includes the pontoon and the annular tension buffer assembly.

It). A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly includes a pipe extending through the buffer assembly whereby the roof decks inside and outside the annular tension buffer assembly communicate with each other.

11. A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly is circular.

12. A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly is polygonal. 

1. A pontoon type floating roof for liquid storage tanks comprising a pontoon, at least one annular tension buffer assembly concentrically disposed within and with respect to the pontoon, and roof decks located at or under the level of liquid stored in a tank extending between the pontoon and the annular tension buffer assembly and also within the annular tension buffer assembly, the roof decks having a lower surface in cOntinuous contact with the stored liquid to prevent the formation and accumulation of vapor under the decks, and wherein the pontoon and the annular tension buffer assembly include elastically deformable side walls to which the roof decks are connected.
 2. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the roof decks are connected to the side wall of the pontoon by means of a ring member having a curved section.
 3. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the roof decks are held by a pair of upper and lower knuckle rings fitted to the side walls of the pontoon whereby the roof decks are integrated with the pontoon.
 4. A pontoon type floating roof for liquid storage tanks as in claim 3 wherein the knuckle rings fitted to the side walls of the pontoon are disposed on the top of the roof decks and integrated with the roof decks.
 5. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the inner portion of the top plate of the pontoon is formed into a knuckle ring and the roof decks are fitted to the ends of this ring.
 6. A pontoon type floating roof for liquid storage tanks as in claim 5 wherein the knuckle ring is a ring of 1/4 round.
 7. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the cross section of the annular tension buffer assembly is cylindrical.
 8. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the cross section of said annular tension buffer assembly is semi-cylindrical.
 9. A pontoon type floating roof for liquid storage tanks as in claim 1 wherein the annular tension buffer assembly is a closed hollow annular structure, and the center portions of the roof decks disposed between the pontoon and the annular tension buffer assembly and within the annular tension buffer assembly are located below a horizontal plane which includes the pontoon and the annular tension buffer assembly.
 10. A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly includes a pipe extending through the buffer assembly whereby the roof decks inside and outside the annular tension buffer assembly communicate with each other.
 11. A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly is circular.
 12. A pontoon type floating roof for liquid storage tanks as in claim 9 wherein the annular tension buffer assembly is polygonal. 